Battery enclosure for sterilizeable surgical tools having  thermal insulation

ABSTRACT

A battery pack assembly or enclosure comprises one or more batteries having an electrochemical cell and an enclosure having at least an outer wall configured to create a sealed volume of space substantially around the batteries. An atmosphere of the volume of space comprises gas having a thermal conductivity less than 0.018 watts per meter per degree Celsius. This atmosphere of gas provides an insulative layer between the outer wall of the enclosure and the batteries. With this insulative layer, the battery pack assembly can be subjected to autoclaving without damaging the batteries. The battery pack assembly can be used to power surgical tools or other devices that are subjected to autoclaving.

RELATED APPLICATION

This application claims the benefit, under 35 U.S.C. §119(e), toprovisional application Ser. No. 62/108,749.

BACKGROUND

The present disclosure relates to the thermal insulation of a batteryenclosure and, for example, to an insulation of an enclosure containingbattery cells that is exposed to high temperatures during operation.

Battery powered tools have provided increased convenience andproductivity to medical professionals in surgical settings. Thesesurgical tools and their associated batteries are sterilized beforeutilization, such as in the sterile field of an operating room. Batterypowered surgical tools are typically designed to withstand thetemperatures associated with an autoclave cycle for sterilizing asurgical tool or instrument. These temperatures may reach, for example,132° C. for several minutes in a pre-vacuum sterilizer or 121° C. for 30minutes or longer in a gravity displacement sterilizer.

Like the surgical tools and instruments, the battery enclosures of suchtools are also sterilized. This sterilization presents a problem as theperformance of rechargeable battery cells can be degraded if they areexposed to temperatures in excess of 70° C. Beyond degraded performance,the battery cells themselves are at risk of being permanently damagedupon exposure to temperatures in excess of 80° C.

One approach to prevent the battery cells from reaching such criticaltemperatures has been to sterilize the battery enclosure without thebattery cells. The battery cells are then added to the enclosure withthe use of shields and sealable covers to prevent exposure of the cellsto the sterile field. Another approach has been to insulate the batterycell with the use of insulation materials, such as microporous silicate(U.S. Pat. No. 6,756,766) or silica (silicon dioxide) or silica ceramiccarbon nitride and silica aerogel (U.S. Pat. No. 8,486,560).

Yet another approach has been to use chemicals and gasses to sterilizethe battery enclosure with the battery cells. This type of sterilizationprocess avoids generating temperatures that could potentially damage thebattery cells. However, this approach requires sterilizationinfrastructure not typically present in hospitals, surgery centers andother healthcare institutions.

SUMMARY

A simple low cost, sealed battery enclosure and associated method ofmanufacture is provided. In the exemplary embodiment, the enclosure canbe autoclaved with the rechargeable battery (electrochemical) cellsenclosed therein.

According to one aspect of the exemplary embodiment , a battery packassembly comprises at least one battery comprising an electrochemicalcell and an enclosure having at least an outer wall configured to createa sealed volume of space substantially around the at least one battery.An atmosphere of the volume of space comprises gas. The thermalconductivity of the gas in the volume of space is less than 0.018 wattsper meter per degree Celsius.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an illustration of a perspective view of a battery packassembly consistent with an aspect of an exemplary embodiment of theinvention;

FIG. 2 is an illustration of a perspective view of a battery packassembly consistent with another aspect of an exemplary embodiment ofthe invention;

FIG. 3 is an illustration of a perspective view of a battery packassembly coupled to a recharging station consistent with an aspect of anexemplary embodiment of the invention;

FIG. 4 is an illustration of a perspective view of a battery packassembly coupled to a surgical device consistent with an aspect of anexemplary embodiment of the invention; and

FIG. 5 is an illustration of a perspective view of a battery packassembly including a display consistent with an aspect of an exemplaryembodiment of the invention.

DETAILED DESCRIPTION

The exemplary embodiments described herein are provided for illustrativepurposes only and are not limiting of the scope of the invention. It isunderstood that various omissions and substitutions of equivalentstructures are contemplated as circumstances may suggest or renderexpedient as known to one of skill in the art. Furthermore, although thefollowing relates substantially to exemplary embodiments of the physicaldesign, it will be understood by those familiar with the art thatchanges to materials, part descriptions and geometries can be madewithout departing from the spirit of the invention.

In one aspect of an exemplary embodiment of the invention, a batterypack assembly or enclosure comprises one or more batteries having anelectrochemical cell and an enclosure having at least an outer wallconfigured to create a sealed volume of space substantially around thebatteries. An atmosphere of the volume of space comprises gas having athermal conductivity less than 0.018 watts per meter per degree Celsius.This atmosphere of gas provides an insulative layer between the outerwall of the enclosure and the batteries. With this insulative layer, thebattery pack assembly can be subjected to autoclaving without damagingthe batteries.

The thermal conductivity of the gas in the volume of space can be lower,such as less than 0.016 watts per meter per degree Celsius. In addition,the atmosphere of the volume of space can include a partial vacuumsufficient to make the thermal conductivity of the gas in the volume ofspace less than 0.018 watts per meter per degree Celsius. The gasincluded in the atmosphere of the volume of space can be at least 25% orat least 33% of an inert gas selected from the group consisting ofkrypton, xenon, argon, and freon.

The battery pack assembly can also include a plurality of standoffs thatseparate the batteries from the outer wall of the enclosure. Inaddition, an inner wall can be included that at least partially enclosesthe batteries. The outer wall of the enclosure is formed from acomposite plastic that can be covered with a coating such as ametallization layer that reduces the permeation rate of the outer wall.

To provide power, the battery pack assembly includes battery terminalsthat extend from the batteries to the exterior of the outer wall. Thebattery terminals include a positive terminal and a negative terminalthat are coupled to electrical contacts, which are configured to connectto and power a surgical tool as well as to connect to and be charged bya recharging station.

As shown in FIG. 1, a battery pack enclosure or assembly 100 includesbattery cells 110, battery terminals 120, a first or outer wall 130, anda second or inner wall 140. The battery cells 110 can be rechargeable,electrochemical batteries, such as lead-acid, nickel cadmium (NiCd),nickel metal hydride (NiMH), lithium ion (Li-ion), or lithium ionpolymer (Li-ion polymer).

The outer wall 130 forms a contiguous, sealed compartment around theinner wall 140 and the battery cells 110. The space between an interiorsurface of the outer wall 130 and an exterior surface of the inner wall140 represents a volume of space 160 having an atmosphere comprisinggas, a partial vacuum, or both. The inner wall 140 can be a contiguousor non-contiguous wall around the battery cells 110. When implemented asa non-contiguous wall, the inner wall 140 can partially or substantiallycover the battery cells 110 and separate them from the interior surfaceof the outer wall 130. The inner wall 140 preferably has across-sectional area that is less than 25% of the exterior area of theouter wall 130. Reducing the cross-sectional area of the inner wall 140with respect to the outer wall 130 helps to minimize conductive heattransfer through the battery pack enclosure 100 from the outer wall 130to the battery cells 110.

To separate the outer wall 130 from the inner wall 140, the battery packenclosure 100 includes a plurality of standoffs, spacing material orseparators 150 that maintain the separation of the outer wall 130 fromthe inner wall 140. In the exemplary embodiment the spacing material isformed of individual standoffs 150 that prevent the battery cells 110from contacting the outer wall 130. Of course, alternative arrangementsare contemplated that provide a filler, or contiguous spacing ratherthan discrete structural “standoffs.” Alternatively, as shown in FIG. 2,the battery pack enclosure 100 can be designed without the inner wall140. In this configuration, the battery cells 110 are exposed to theatmosphere in the volume of space 160. Without the inner wall 140, thestandoffs 150 are arranged to separate the outer wall 130 from thebattery cells 110, as shown in FIG. 2.

The standoffs 150 are preferably formed from a material having a lowthermal conductivity material, which helps to reduce heat transfer fromthe outer wall 130 to the inner wall 140 and the battery cells 110. Inaddition, the cross-sectional area of the standoffs 150 is preferablyminimized. For example, the cross-sectional area can be a fraction ofthe surface area of the battery cells 110, such as less than 10%. Thenumber of standoffs 150 included within the battery pack enclosure 100depends on the particular configuration of the battery cells 110, butthe number of standoffs 150 is preferably a number sufficient tomaintain the position of the battery cells 110 (or inner wall 140 ifincluded) within and away from the outer wall 130.

Whereas the exterior surface of the outer wall 130 is exposed to theenvironment, the interior surface of the outer wall 130 is exposed tothe atmosphere in the volume of space 160 between the outer wall 130 andthe inner wall 140 or battery cells 110. This atmosphere provides aninsulative layer between the outer wall 130 and the battery cells 110.The atmosphere of gas can comprise, for example, at least 25% of a lowthermal conductivity gas. The low thermal conductivity gas can compriselarger portions of the atmosphere, such as at least 33%, at least 50%,or all of the atmosphere in the volume of space 160. The low thermalconductivity gas is preferably an inert gas such as Argon, Krypton,Xenon, or Freon.

In addition to the low thermal conductivity gas, or as an alternative tothe low thermal conductivity gas, the atmosphere in the volume of space160 can comprise a partial vacuum. The partial vacuum preferably amountsto at least 25% of the atmosphere in the volume of space 160. Thepartial vacuum can comprise larger portions of the atmosphere, such asat least 33%, at least 50%, or all of the atmosphere in the volume ofspace 160.

The partial vacuum helps to reduce heat transfer from the outer wall 130to the battery cells 110 because heat transfer at atmospheric pressureis predominantly affected by either direct transfer during gasmolecule-to-molecule collisions or by molecular motion convection. Iftwo objects, such as the outer wall 130 and the battery cells 110, areat different temperatures and placed in a chamber at atmosphericpressure, heat will begin to flow from the hotter to the colder throughthe gas molecules. If such pressure is reduced by removing some of thegas molecules, such as by introducing a partial vacuum, the distancebetween the molecules will become greater and the number of molecularcollisions will become decrease, thereby resulting in a reduction ofheat flow. Lowering the thermal conductivity of the heat transfer medium(such as the gas molecules) permits the hotter object to retain itsheat. Moreover, if the pressure is continually reduced, the heat flowwill similarly be continually reduced. Thus, introducing at least apartial vacuum between the hot and cold objects (e.g., the outer wall130 and the battery cells 110) creates a thermal insulator. The amountof insulation provided by the partial vacuum depends on the amount ofthe vacuum (i.e., the paucity of molecules) between the hot and coldobjects.

Whether the atmosphere in the volume of space 160 comprises a lowthermal conductivity gas, a partial vacuum, or a combination of them,the thermal conductivity for the atmosphere is preferably configured toinsulate the battery cells sufficiently to protect the battery cells 110from being damaged during an autoclave cycle. The thermal conductivityof air is 0.024 watts per meter degree Celsius. Using the low thermalconductivity gas and/or partial vacuum reduces the thermal conductivityof the atmosphere in the volume of gas 160 to be lower than the thermalconductivity of air. To provide protection to the battery cells 110,sufficient low thermal conductivity gas and/or partial vacuum ispreferably provided in the atmosphere to make the range of thermalconductivity for the atmosphere, for example, from 0.002 to 0.018 wattsper meter degree Celsius. More preferably, the thermal conductivity ofthe atmosphere is less than 0.018, less than 0.016, less than 0.012,less than 0.009, or less than 0.007 watts per meter per degree Celsius.In an exemplary embodiment, the low thermal conductivity gas has athermal conductivity of less than 0.012 watts per meter degree Celsiussuch as Freon (having a thermal conductivity of 0.007) or Krypton(having a thermal conductivity of 0.009.) With the atmosphere of thevolume of space 160 configured to have a low thermal conductivity, thebattery pack enclosure 100 prevents, for example, the inner wall 130 andthe battery cells 120 from reaching 70° C. when the outer wall isexposed to 132° C. for four minutes or 121° C. for 30 minutes.

To provide further protection of the battery cells 110 beyond theinsulative layer provided by the atmosphere in the volume of space 160,the walls of the battery pack enclosure 100 can comprise a materialhaving a very low permeation rate to gases including Nitrogen, Oxygenand any other gas present in the atmosphere. The material preferably hasa very low permeation rate both at room temperature as well as atautoclave temperatures, such as 132° Celsius. The material for the outerwall 130 and inner wall 140 can be, for example, a composite plastichaving different webs and layers to reduce permeability. The thicknessof the outer wall 130 is preferably sufficient to withstand damage, suchas from being dropped on a floor, as well as to account for the impactand molding characteristics of the material used, such as plastic.

In addition to the material for the walls of the battery pack enclosure100, a membrane, coating, co-extrusion or plating can be provided on theinterior or exterior of the outer wall 130, and optionally to the innerwall 140 as well. The coating is preferably located at least on theinterior of the outer wall 130 to protect from damage, such as fromscratching. The coating, which can be a metallization layer for example,helps to decrease the permeation rate of the walls, preferably by atleast 90%. The desired low permeation rate will generally be a functionof the “free gas volume” inside the outer wall 130 of the battery packenclosure 100. In a preferred embodiment, for example, the material ofthe outer wall 130 and the coating are preferably designed to permit atransfer of no more than 10% of the free volume within the atmosphere ofthe volume of space 160 within one year when stored at 23° C. With sucha low permeation rate, the atmosphere within the volume of space 160does not dissipate from the battery pack enclosure 100 over time.

The battery terminals 120 can include positive and negative leads thatcan connect to electrical contacts 170. The electrical contacts 170 areconfigured to connect and provide power to a device such as a surgicaltool, such as shown in FIG. 4. The surgical tool can be, for example, anorthopedic power tool such as the one described in U.S. Pat. No.8,936,106. The electrical contacts 170 can also connect to a batterycharger to recharge the battery cells 110, such as shown in FIG. 3. Thebattery terminals 120, which pass through the outer wall 130 and theinner wall 140, are preferably sealed by a low permeability pottingcompound, O-ring or other sealing method to minimize gas leakage. Thesealing material can be, for example, 20-2350 polyurethane.Additionally, the cross-sectional area of the electrical contacts 170 iskept at a minimum in order to reduce conductive heat transfer to thebattery cells 110.

In addition to the positive and negative leads, the battery terminals120 can also include one or more communication terminals. Thesecommunication terminals can be configured to provide information aboutbreaches of the atmosphere, the temperature of the battery cells 110,the charge level of the battery cells, and any other informationrelevant to the operation or condition of the battery pack enclosure 100including the battery cells 110. To provide this information via thecommunication terminals, the battery pack enclosure 100 can includecircuitry, detectors, and transducers configured to detect theconditions and parameters related to the operation of the battery packenclosure 100 and the battery cells 110. The communication terminals canbe coupled to a display 180, such as shown in FIG. 5, which isconfigured to display information provided by the communicationterminals. A fuel cell may also be substituted for the electro-chemicalbattery cell.

To detect temperature, the batter pack enclosure 100 can include athermal couple that monitors the temperature of the battery cells 1120or the area around the battery cells 110. Indicator lights visible onthe exterior surface of the outer wall 130 or sounds from a speakermounted on the exterior surface of the outer wall may be used toindicate the status of the temperature, such as if the temperatureremains at an acceptable level, has reached a point approaching criticallevel, or has reached a critical level. The indicator lights and soundcan also be used to indicate whether a battery is ready to be used ornot. A thermochromic strip can also be provided that indicates via coloror other change that the battery cells 110 are at a safe operatingtemperature.

Besides detecting and providing indications of temperature, the batterypack enclosure 100 can include a failsafe that, when activated, preventsthe battery from being used. The failsafe can be implemented, forexample, by blowing a fuse in the connection. Additional safetiescommonly used in the industry, such as PTC elements, may be incorporatedin the battery pack enclosure 100 to prevent the battery cells 110 frombeing discharged until they have cooled sufficiently. The battery packenclosure 100 can also include a sensor for detecting the thermalconductivity of the internal gas chamber area and a sensor for detectingthe peak temperature reached by the battery cells 110 within the batterypack enclosure 100 during an autoclave cycle. Based on the detectedinformation, the sensors can communicate information to an operator,such as a breach in the thermal insulation system or a defect with thebattery cells 110, e.g., that the battery cells 110 will not charge.

Although there have been described particular embodiments of the presentdisclosure, it is not intended that such references be construed aslimitations on the scope of the disclosure.

What is claimed is:
 1. A battery pack assembly comprising: at least onebattery comprising an electrochemical cell; an enclosure having at leastan outer wall configured to create a sealed volume of spacesubstantially around the at least one battery; wherein an atmosphere ofthe volume of space comprises gas, wherein the thermal conductivity ofthe gas in the volume of space is less than 0.018 watts per meter perdegree Celsius.
 2. The battery pack assembly of claim 1, wherein thethermal conductivity of the gas in the volume of space is less than0.016 watts per meter per degree Celsius.
 3. The battery pack assemblyof claim 1, wherein an atmosphere of the volume of space includes apartial vacuum sufficient to make the thermal conductivity of the gas inthe volume of space less than 0.018 watts per meter per degree Celsius.4. The battery pack assembly of claim 1, wherein an atmosphere of thevolume of space includes at least 25% of an inert gas selected from thegroup consisting of krypton, xenon, argon, and freon.
 5. The batterypack assembly of claim 1, wherein an atmosphere of the volume of spaceincludes at least 33% of an inert gas selected from the group consistingof krypton, xenon, argon, and freon.
 6. The battery pack assembly ofclaim 1, further comprising a plurality of standoffs that separate theat least one battery from the outer wall of the enclosure.
 7. Thebattery pack assembly of claim 6, wherein the enclosure furthercomprises an inner wall at least partially enclosing the at least onebattery, wherein the plurality of standoffs separate the inner wall fromthe outer wall.
 8. The battery pack assembly of claim 1, wherein theouter wall of the enclosure is formed from a composite plastic.
 9. Thebattery pack assembly of claim 8, wherein at least one of an exteriorsurface and an interior surface of the outer wall of the enclosureincludes a coating that reduces the permeation rate of the outer wall.10. The battery pack assembly of claim 9, wherein the coating includes ametallization layer.
 11. The battery pack assembly of claim 1, furthercomprising battery terminals, wherein the battery terminals extend fromthe at least one battery to the exterior of the outer wall.
 12. Thebattery pack assembly of claim 11, wherein the battery terminalscomprise a positive terminal, a negative terminal, and a communicationterminal.
 13. The battery pack assembly of claim 11, wherein thecommunication terminal provides information regarding the temperature ofthe at least one battery.
 14. The battery pack assembly of claim 11,further comprising a sensor that detects the thermal conductivity withinthe volume of space, wherein the sensor provides information via thecommunication terminal of a breach of the battery pack assembly based onthe detected thermal conductivity.
 15. The battery pack assembly ofclaim 11, further comprising a sensor that detects a peak temperaturereached by the at least one battery during an autoclave cycle, whereinthe sensor provides information via the communication terminal of thedetected peak temperature.
 16. The battery pack assembly of claim 12,further comprising electrical contacts coupled to the positive terminaland the negative terminal.
 17. The battery pack assembly of claim 16,wherein the electrical contacts are configured to connect to arecharging station.
 18. The battery pack assembly of claim 1, wherein atemperature of the at least one battery remains below 70° C. when theouter wall is exposed to 132° C. for four minutes.
 19. The battery packassembly of claim 1, wherein a temperature of the at least one batteryremains below 70° C. when the outer wall is exposed to 121° C. for 30minutes.
 20. A surgical tool comprising: a battery pack assembly havingat least one battery comprising an electrochemical cell and an enclosurecomprising at least an outer wall configured to create a sealed volumeof space substantially around the at least one battery; wherein anatmosphere of the volume of space comprises gas, wherein the thermalconductivity of the gas in the volume of space is less than 0.018 wattsper meter per degree Celsius, and wherein the battery pack assemblyprovides power for the operation of the surgical tool.